Vulvar squamous cell carcinoma development after diagnosis of VIN increases with age.

Objective: The purpose of the present study is to investigate the trends in incidence of both usual (u) and differentiated (d) vulvar intraepithelial neoplasia (VIN) separately, their malignant potential and the relation with other HPV related anogenital lesions in the Netherlands during a 14-year-period.
Methods: The incidences of both types of VIN and vulvar SCC were retrieved from the Nationwide Netherlands Database of Histo- and Cytopathology. Population data were retrieved from the Database of Statistics Netherlands.
Results: In the study period, the incidence of uVIN and dVIN increased, while the incidence of vulvar SCC remained stable. The overall percentage of uVIN patients that were later diagnosed with vulvar SCC was 5.7%, which was significantly lower than the percentage for dVIN patients (32.8%). In addition to this 5.6-fold increased conversion rate, the time of progression from dVIN to SCC development was significantly shorter than that of uVIN (p=0.005). Percentage of uVIN patients that were later diagnosed with SCC significantly increased with age (p=0.005), whereas the time to SCC significantly shortened with age (p=0.05). Forty-one percent of uVIN patients had a past, concomitant or future HPV-associated lesion of the lower genital tract, which is in contrast to the 3% for dVIN patients.
Conclusions: An increase in diagnoses of both uVIN and dVIN has not led to an increase in vulvar SCC incidence. The malignant potential of dVIN is higher than that for uVIN. For uVIN the malignant potential increases with age.